In the analysis of a subterranean formation, an imager deployed in a wellbore penetrating the formation may be utilized to obtain an image of the resistivity profile of the formation, such as may range between about one ohm-meter and about 1,000 ohm-meters. For example, the imager may comprise a button electrode and a return electrode and utilize a voltage source coupled to one of the electrodes to inject an excitation voltage VE into the formation. The resulting current circulating between the electrodes is then measured through a sampling resistor electrically coupled to the voltage source. The measured current provides information indicative of the formation resistivity.
When drilling is performed using oil-based mud (OBM), the imager may measure the formation resistivity through a dielectric fluid, such as oil and/or drilling fluid, which occupies a standoff between electrodes of the OBM imager and the sidewall of the wellbore. Such standoff may range between about three millimeters (mm) and about thirty mm, and makes it more difficult to obtain the formation resistivity accurately. The OBM imager may utilize high frequencies to enhance the accuracy of the measurements.